Landline phones in the Christchurch area are working: Telecom says its fixed-line network has been largely unaffected and its lines maintenance company Chorus says backup power is in place.
There is some disruption, however, to parts of the mobile network. Civil Defence says there may not be full coverage in parts of the city, because cellphone towers are operating on battery power.
Telecom communications manager Mark Watts says fixing the mobile networks is largely dependent on electricity being restored, and if people have old analog phones they should use them.
Vodafone is urging customers to make calls only in emergencies, and in other cases to send text messages and keep calls to a minimum. Spokesperson Paul Brislen says generators are being sent from as far away as Wellington.
Civil Defence Minister John Carter is asking people in the quake-affected area to avoid using their telephones unless it is necessary. He told the Morning Report special that people trying to contact loved ones could overload the system.
The broadcast infrastructure provider Kordia says it's giving assistance where needed to keep critical local transmission systems operating. It says television and radio transmitters are working off diesel generators.